White Light Emitting Device and Diffusing Layer

ABSTRACT

There is provided a white light emitting device comprising a first LED and a second LED disposed on a substrate, a first photoluminescence material layer disposed over at least said first LED, a second photoluminescence material layer disposed over at least said second LED, and a diffusing layer disposed over said first and second photoluminescence layers, said diffusing layer comprising light scattering particles. A method and component are also provided.

FIELD OF THE INVENTION

Embodiments of the present invention are directed to white lightemitting devices; in particular, although not exclusively, to colortunable white light emitting devices. More particularly, although notexclusively, embodiments concern white light emitting devices comprisinga diffusing layer.

BACKGROUND OF THE INVENTION

White light emitting LEDs (“white LEDs”) include one or morephotoluminescence materials (typically inorganic phosphor materials),which absorb a portion of the excitation light (typically blue) emittedby the LED and re-emit light of a different color (wavelength). Theportion of the blue light generated by the LED that is not absorbed bythe photoluminescence material combined with the light emitted by thephotoluminescence material provides light which appears to the eye asbeing white in color. Due to their long operating life expectancy(>50,000 hours) and high luminous efficacy (100 lumens per watt andhigher), white LEDs are rapidly replacing conventional fluorescent,compact fluorescent and incandescent lamps.

A color tunable white light emitting device typically comprises multipleLEDs. There are various forms of color tunable LEDs. One form is ChipScale Packaging (CSP) in which each LED Chip (Die) is individuallycoated with the photoluminescence material. Typically, multiple CSP LEDsare then packaged to form the color tunable white light emitting device.While this form of LED generates white light having good coloruniformity, it is relatively expensive to manufacture since each LEDChip requires an individual uniform thickness coating ofphotoluminescence material. Since the manufacturing process takes moretime due to the intricacies involved in individually coating each LEDChip, this process is expensive. Moreover, CSP can require the use ofmore photoluminescence material, thereby further increasing costs. Theluminous efficacy of CSP LEDs can be relatively lower compared withother LED forms.

Another form of color tunable white light emitting devices is Chip onBoard (COB) in which multiple LED Chips (Dies) are located on asubstrate before one or more photoluminescence materials is disposedthereon. The luminous efficacy of white light emitting devices in theform of COB is generally superior to the luminous efficacy of whitelight emitting devices in the form of CSP. However, COB LEDs can sufferfrom generation of white light having low color uniformity compared withother forms.

The present invention intends to address and/or overcome the limitationsdiscussed above by presenting new designs and method not hithertocontemplated nor possible by known constructions. More particularly,there is a need for a cost-effective white light emitting device thatgenerates light with improved color uniformity.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided awhite light emitting device comprising a first LED and a second LEDdisposed on a substrate, a first photoluminescence material layerdisposed over at least said first LED, a second photoluminescencematerial layer disposed over at least said second LED, and a diffusinglayer disposed over said first and second photoluminescence layers, saiddiffusing layer comprising light scattering particles.

The white light emitting device formed according to an embodiment of thepresent invention exhibits enhanced color uniformity of generated whitelight due to the combination of the first/second photoluminescencematerial layers and the diffusing layer disposed thereover. Enhancedcolor uniformity is particularly advantageous when the device is used inlarge beam optics. Moreover, compared with CSP LEDs, for example, theamount of photoluminescence material used may also be reduced therebyproviding a more cost-effective manner of manufacturing the white lightemitting device. This is because the diffusing layer comprising lightscattering particles increases the probability that a photon will resultin the generation of photoluminescence light by directing light backinto the first or second photoluminescence layers. Thus, the amount ofphotoluminescence material required to generate a given colortemperature of light can be reduced since more of the first/second LEDlight is converted to photoluminescence light owing to the diffusinglayer.

Further, COB LEDs provided with a diffusing layer thereon are able togenerate white light having a luminous efficacy that is comparable orgreater than white light generated by CSP LEDs.

Hence, the present invention is the provision of a white light emittingdevice that does not suffer from the disadvantages discussed above suchas high cost of manufacture and low color uniformity of white lightgenerated.

It may be that the first photoluminescence material layer comprises afirst phosphor material and/or the second photoluminescence materiallayer comprises a second phosphor material. The first and secondphosphor materials may be different. It may be that the firstphotoluminescence material layer comprises a first quantum dot material(QD) and/or the second photoluminescence material layer comprises asecond quantum dot (QD) material.

The first phosphor material may be excitable to generate white lighthaving a correlated color temperature of 2700K to 3500K.

The second phosphor material may be excitable to generate white lighthaving a correlated color temperature of 5000K to 6500K.

In this way, the white light emitting device may be a color temperaturetunable white light emitting device.

The white light emitting device may comprise alternating arrays of firstLEDs and second LEDs. Such a white light emitting device lends itself toa tunable configuration in which the arrays of the first and second LEDscan be arranged according to the desired requirements of light to begenerated.

More particularly, the white light emitting device may comprisealternating strips of the first and second photoluminescence materiallayers associated with the alternating arrays of first LEDs and secondLEDs. Such an arrangement is particularly advantageous because itsimplifies the manufacturing process thereby reducing costs. Forexample, compared to CSP LEDs which are individually coated with aphotoluminescence material, the inventors have discovered that disposingthe first and second photoluminescence materials as “layers” in the formof alternating strips over the first and second LEDs is significantlymore time-efficient and cost-effective. That is a plurality offirst/second LEDs can be covered/disposed with a first/secondphotoluminescence material rather that coating each LED individually.

The diffusing layer may be in direct contact with the first and/orsecond photoluminescence material layer. This may improve the amount oflight being scattered by the light scattering particles.

The diffusing layer may comprise a light transmissive material and lightscattering particles. The light transmissive material may allow thelight scattering material to be suspended therein.

It may be that the light scattering particles are incorporated in thelight transmissive material. This may simplify the manufacturing processof the diffusing layer and improve its robustness and reliability.

The light scattering particles may be substantially uniformlydistributed through the light transmissive material. Having uniformlydistributed light scattering particles within the light transmissivematerial may enhance the uniformity of light generated by the whitelight emitting device.

The diffusing layer may comprise a layer of the light transmissivematerial and a layer of the light scattering particles. The layer oflight scattering particles can be deposited directly onto the lightlayer of light transmissive material by for example screen printing.Alternatively, the layer of light scattering particles can bemanufactured separately. This alternative configuration may provide moreflexibility in the way the diffusing layer is manufactured, since thelight transmissive layer and the layer of light scattering particles maybe separately manufactured before assembly, which could be morecost-effective is some instances.

It may be that the layer of the light transmissive material is disposedbetween the layer of the light scattering particles and the first and/orsecond photoluminescence material layers. Such a configuration mayprovide greater distance between the light scattering particles and thefirst and/or second photoluminescence material layers and this canimprove color uniformity since color mixing of light can occur withinthe layer of light transmissive material.

The layer of the light scattering particles may be disposed between thelayer of the light transmissive material and the first and/or secondphotoluminescence material layers. In such a configuration, the layer oflight transmissive material may act as a protective layer to the layersof the light scattering particles and the first and/or secondphotoluminescence material layers. It may be that the layer of lighttransmissive is the outermost layer or faces outwardly.

The diffusing layer may comprise two layers of the light transmissivematerial and a layer of the light scattering particles disposedtherebetween. This configuration may provide a greater distance betweenthe light scattering particles and the first and/or secondphotoluminescence material layers, as well as the layer of lighttransmissive material may acting as a protective layer.

It may be that at least one of the first photoluminescence materiallayer, the second photoluminescence material layer, or the diffusinglayer comprises light scattering particles. Thus, light scatteringparticles may be contained in the first photoluminescence material layerand the diffusing layer; in the second photoluminescence material layerand the diffusing layer; or in the first photoluminescence materiallayer, the second photoluminescence material layer and the diffusinglayer. The inclusion of light scattering particles in the first and/orsecond photoluminescence material layers increases the probability thata photon will result in the generation of photoluminescence lightthereby reducing the amount of photoluminescence material required.Further, this inclusion of light scattering particles in thephotoluminescence layer(s) may improve the uniformity of the white lightgenerated by the light emitting device generated still further.

The first photoluminescence material layer and/or the secondphotoluminescence material layer may comprise light scattering particlesincorporated in a light transmissive material. The light transmissivematerial may allow the light scattering particles to be distributed moreuniformly by suspension therein, for instance.

The white light emitting device of claim 1, wherein the substrate islight transmissive. The substrate can comprise a circuit board such as ametal core printed circuit board (MCPCB).

The light scattering particles may have an average particle sizeselected such that they scatter excitation light generated by the firstand second LEDs relatively more than they scatter light generated by thefirst and second photoluminescence material layers, optionally theaverage particle size may be in a range from about 100 nm to about 200nm.

One benefit of this approach, especially within the diffuser layer, isthat by selecting an appropriate particle size and concentration perunit area of the light scattering particles, an improvement is obtainedin the white color appearance of an LED device in its OFF state. Anotherbenefit is an improvement to the color uniformity of emitted light fromthe white light emitting device for emission angles over a ±60° rangefrom the emission axis. Moreover, the use of a diffusing layer having anappropriate particle size and concentration per unit area of the lightscattering particles can substantially reduce the quantity ofphotoluminescence material required to generate a selected color ofemitted light, since the diffusing layer increases the probability thata photon will result in the generation of photoluminescence light bydirecting light back into the photoluminescence layer(s). It may be thatinclusion of a diffusing layer in direct contact with thephotoluminescence layer(s) can reduce the quantity of phosphor materialrequired to generate a given color emission product, e.g. by up to 40%.As used herein, “direct contact” means that there are no interveninglayers or air gaps.

The light transmissive medium may be disposed between the diffusinglayer and the first and/or second photoluminescence layers.

The amount of light scattering particles may vary across the diffusinglayer. For instance, there may be more light scattering particlestowards the center of the light emitting device than its edges. Thecenter of the light emitting device may be considered the center of thesubstrate, for instance.

The thickness of the diffusing layer may vary.

The concentration of light scattering particles within the diffusinglayer may vary.

By varying the thickness of the light diffusing layer and/or theconcentration of light scattering particles within the diffusing layer,the light scattering properties can be appropriately selected dependingon the desired output of the white light emitting device.

The light scattering particles may comprise titanium dioxide (TiO₂),barium sulfate (BaSO₄), magnesium oxide (MgO), silicon dioxide (SiO₂) oraluminum oxide (Al₂O₃), for example.

The light transmissive material may comprise a curable liquid polymersuch as a polymer resin, a monomer resin, an acrylic, an epoxy, asilicone or a fluorinated polymer.

The substrate may comprise a circuit board such as a metal core printedcircuit board (MCPCB).

In another aspect, the present invention encompasses a method ofmanufacturing a white light emitting device, comprising the steps of:providing an array of first LEDs; dispensing a first photoluminescencematerial layer at least over said array of first LEDs; providing anarray of second LEDs; dispensing a second photoluminescence materiallayer at least over said array of second LEDs; and dispensing adiffusing layer over said first and second photoluminescence materiallayers.

To reduce the variation in emitted light color with emission angle, theweight loading of light scattering particles to light transmissivematerial may be in a range from 0.1 to 50% wt or 5 to 10% wt.

In another aspect, the present invention envisages a white lightemitting device comprising alternating arrays of first LEDs and secondLEDs disposed on a substrate, a first photoluminescence material layerdisposed over at least said array of first LEDs, a secondphotoluminescence material layer disposed over at least said array ofsecond LEDs, and a diffusing layer disposed over said first and secondphotoluminescence material layers, the diffusing layer comprising lightscattering particles, wherein the first photoluminescence material layercomprises a first phosphor material excitable to generate white lighthaving a first correlated color temperature, the secondphotoluminescence material layer comprises a second phosphor materialexcitable to generate white light having a second correlated colortemperature.

It may be that the first phosphor material is excitable to generatewhite light having a correlated color temperature of 2700K to 3500Kand/or the second phosphor material is excitable to generate white lighthaving a correlated color temperature of 5000K to 6500K.

According to another aspect of the present invention, there is provideda component for a white light emitting device, comprising alternatingstrips of first and second photoluminescence material layers disposed ona substrate, and a diffusing layer disposed over said alternating stripsof first and second photoluminescence material layers, the diffusinglayer comprising light scattering particles, wherein the firstphotoluminescence material layer comprises a first phosphor materialexcitable to generate white light having a first correlated colortemperature, and the second photoluminescence material layer comprises asecond phosphor material excitable to generate light having a secondcorrelated color temperature.

It may be that the first correlated color temperature is from 2700K to3500K and/or the second correlated color temperature is from 5000K to6500K.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the present invention willbecome apparent to those ordinarily skilled in the art upon review ofthe following description of specific embodiments of the invention inconjunction with the accompanying figures, wherein:

FIG. 1 is a sectional view of a white light emitting device inaccordance with an embodiment of the invention;

FIG. 2 is a sectional view of the white light emitting device of FIG. 1with color tunable control;

FIG. 3A is a plan view of a white light emitting device in accordancewith an embodiment of the invention;

FIG. 3B is cross sectional side view through A-A;

FIG. 4 is a plan view of a white light emitting device in accordancewith an embodiment of the invention;

FIG. 5 is a sectional view of a diffusing layer in accordance with anembodiment of the invention;

FIG. 6 is a sectional view of a diffusing layer in accordance withanother embodiment of the invention;

FIG. 7 is a sectional view of a diffusing layer in contact withphotoluminescence material layers in accordance with an embodiment ofthe invention;

FIG. 8 is a sectional view of a diffusing layer in contact withphotoluminescence material layers in accordance with another embodimentof the invention;

FIG. 9 is a sectional view of a diffusing layer in accordance withanother embodiment of the invention;

FIG. 10 is a sectional view of a diffusing layer in accordance withanother embodiment of the invention;

FIG. 11 is a sectional view of a diffusing layer in accordance withanother embodiment of the invention;

FIG. 12 is a sectional view of a diffusing layer in contact withphotoluminescence material layers in accordance with another embodimentof the invention;

FIG. 13 is a sectional view of a diffusing layer in contact withphotoluminescence material layers in accordance with another embodimentof the invention; and

FIG. 14 is a sectional view of a component and a separate LED array fora white light emitting device in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the drawings, which are provided as illustrativeexamples of the invention so as to enable those skilled in the art topractice the invention. Notably, the figures and examples below are notmeant to limit the scope of the present invention to a singleembodiment, but other embodiments are possible by way of interchange ofsome or all of the described or illustrated elements. Moreover, wherecertain elements of the present invention can be partially or fullyimplemented using known components, only those portions of such knowncomponents that are necessary for an understanding of the presentinvention will be described, and detailed descriptions of other portionsof such known components will be omitted so as not to obscure theinvention. In the present specification, an embodiment showing asingular component should not be considered limiting; rather, theinvention is intended to encompass other embodiments including aplurality of the same component, and vice-versa, unless explicitlystated otherwise herein. Moreover, applicants do not intend for any termin the specification or claims to be ascribed an uncommon or specialmeaning unless explicitly set forth as such. Further, the presentinvention encompasses present and future known equivalents to the knowncomponents referred to herein by way of illustration. Throughout thisspecification like reference numerals are used to denote like parts.

A white light emitting device 10 in accordance with an embodiment of theinvention will now be described with reference to FIG. 1 which show asectional side view of the device.

The device 10 comprises first LEDs 12 and second LEDs 14 disposed on asubstrate 16 (e.g. MCPCB); a first photoluminescence material layer 18disposed over at least said first LEDs 12; a second photoluminescencematerial layer 20 disposed over at least said second LEDs 14; and adiffusing layer 22 disposed over said first and second photoluminescencelayers 18, 20; said diffusing layer 22 comprising light scatteringparticles 24.

More particularly, FIG. 1 shows a sectional view of two rows of firstLEDs 12 adjacent two rows of second LEDs 14 in a chip on board (COB)type arrangement. Only one LED of each row is shown in FIGS. 1 and 2;there being a total of four rows (two for first LEDs 12 and two rows forsecond LEDs 14). In this embodiment, the first and second LEDs 12, 14are InGaN (indium gallium nitride) blue LEDs which are operable togenerate blue light having a peak wavelength in a wavelength range 400to 480 nm (typically 450 to 470 nm). The two rows of first LEDs 12 andtwo rows of second LEDs 14 are deposited on a planar substrate 16.Towards the edges of the planar substrate 16 is located a peripheralwall 26 which surrounds (encloses) the two rows of first LEDs 12 and tworows of second LEDs 14. Typically, the wall 26 surrounds the two rows offirst LEDs 12 and two rows of second LEDs 14. In other embodiments, thewall may delineate one or more sides of the substrate.

A first photoluminescence material layer 18 comprising a first phosphormaterial (typically green and red emitting phosphor materials) isdeposited onto the planar substrate 16 and, in this embodiment,completely covers the two rows of first LEDs 12. The first phosphormaterial is excitable to generate white light having a correlated colortemperature of about 2700K to 3500K (warm white light). Similarly, thesecond photoluminescence material layer 20 comprising a second phosphormaterial (Typically a green phosphor material) is deposited onto theplanar substrate 16 and, in this embodiment, completely covers the tworows of second LEDs 14. The second phosphor material is excitable togenerate white light having a correlated color temperature of 5000K to6500K (cool white light). In this way, the first and secondphotoluminescence material layers 18, 20 are located adjacent oneanother and also contained within the wall 26.

A planar diffusing layer 22, having similar dimensions to those of theplanar substrate 16, is disposed over and on top of both the firstphotoluminescence material layer 18 and second photoluminescencematerial layer 20, and is also contained inside the wall 26. The uppersurfaces 28 of the upright walls 26 together with the upper surface 30of the planar diffusing layer 22 define a flush surface. The planardiffusing layer 22, the planar substrate 16, and wall 26 define aninterior volume 32 which houses and encloses the first and secondphotoluminescence material layers 18, 20 and the two rows of first LEDs12 and the two rows of second LEDs 14.

The white light emitting device 10, to an observer 34, exhibits enhancedcolor uniformity of generated white light due to the combination of thefirst and second photoluminescence material layers 18, 20 and thediffusing layer 22 disposed thereover. Compared with CSP LEDs, forexample, the amount of photoluminescence material used may also bereduced thereby providing a more cost-effective manner of manufacturingthe white light emitting device 10. This is because the diffusing layer22 comprising light scattering particles 24 increases the probabilitythat a photon will result in the generation of photoluminescence lightby directing light back into the first or second photoluminescencelayers. Thus, the amount of photoluminescence material required togenerate a given color temperature of light can be reduced since more ofthe first/second LED 12, 14 light is converted to photoluminescencelight owing to the diffusing layer 22.

Referring now to FIG. 2, there is shown the white light emitting deviceof FIG. 1 with dimming control. The first and second photoluminescencematerial layers 18, 20 are operable to absorb a proportion of the bluelight λ₁ generated by the two rows of first LEDs 12 and the two rows ofsecond LEDs 14 and convert it to light of a different wavelength by aprocess of photoluminescence. In this embodiment, the firstphotoluminescence material layer 18 converts the blue light λ₁ to λ₂,and the second photoluminescence material layer 18 converts the bluelight λ₁ to λ₃. Not all of the blue light λ₁ generated by the two rowsof first LEDs 12 and the two rows of second LEDs 14 is absorbed by thefirst and second photoluminescence material layers 18, 20 and some of itis emitted through the diffusing layer 22. The emission product 36 ofthe white light emitting device 10 thus comprises the combined light ofwavelengths λ₁, λ₂, λ₃ generated by the by the two rows of first LEDs 12and the two rows of second LEDs 14 and the first and secondphotoluminescence material layers 18, 20. The CCT of the emissionproduct 36 is thus a combination of the CCT of light (λ₁) generated bythe two rows of first LEDs 12 and the two rows of second LEDs 14, theCCT of light (λ₂) generated by the first photoluminescence materiallayer 18, and the CCT of light (λ₃) generated by the secondphotoluminescence material layer 20.

In this embodiment, the combination of light (λ₁) generated by the tworows of first LEDs 12 and light (λ₂) generated by the firstphotoluminescence material layer 18 generates light having a CCTcorresponding to a warm yellowish white (a correlated color temperatureof about 2700K to 3500K). Similarly, the combination of light (λ₁)generated by the two rows of second LEDs 14 and light (λ₃) generated bythe second photoluminescence material layer 20 generates light having aCCT corresponding to a cool blueish white (a correlated colortemperature of about 5000K to 6500K). Therefore, the emission product 34of the white light emitting device 10 in this example would be acombination of the warm yellowish white light deriving from (λ₁)/(λ₂),the cool blueish white light deriving from (λ₁)/(λ₃).

A dimmer switch 38 may be operably connected to a control circuit 40which is operably connected to the two rows of first LEDs 12 and the tworows of second LEDs 14. The dimmer switch 38 is configured to generate acontinuous range of output powers to be used for controlling (tuning)the color temperature and dimming level of the white light emittingdevice 10. The control circuit 40 is configured to translate thegenerated output power into an on/off arrangement and/or adjustablepower arrangement for the two rows of first LEDs 12 and the two rows ofsecond LEDs 14.

While the variation in color temperature of an incandescent light bulbis directly related to the output power of the dimmer switch, the CCT ofthe emission product 36 of the light emitting device 10 is not directlyrelated to the output power of the dimmer switch 38. As such, thecontrol circuit 40 must translate the output power of the dimmer switch38 into a control arrangement for the two rows of first LEDs 12 and thetwo rows of second LEDs 14 such that the white light emitting device 10dimming behavior resembles that of a dimmable incandescent lightbulb—that is on dimming its color temperature changes from cool white atfull power to warm white when dimmed.

Because the emission product 36 of the white light emitting device 10 isa combination of light (λ₁) generated by the two rows of first LEDs 12and the two rows of second LEDs 14 and light (λ₂, λ₃) generated by thefirst and second photoluminescence material layers 18, 20, the CCT ofthe emission product 36 can be changed by modifying the combination oflight. In this way, a CCT corresponding to a warm yellowish white colormay be generated by having a larger portion of the emission product 36originate from the first photoluminescence material layer 18 (e.g.,region generating light with a CCT corresponding to a warm yellowishwhite) and a smaller portion of the emission product 36 originate fromthe second photoluminescence material layer 20 (e.g., region generatinglight with a CCT corresponding to a cool blueish white). A CCTcorresponding to a cool bluish white color may be generated by having asmaller portion of the emission product 36 originate from the firstphotoluminescence material layer 18 and a larger portion of the emissionproduct 36 originate emanate from the second photoluminescence materiallayer 20.

The emission product 36 may be modified, for example, by altering theon/off configuration of the two rows of first LEDs 12 and the two rowsof second LEDs 14. Thus, the CCT of the emission product 36 may growcloser to a warm yellowish color as some or all of the second LEDs 14corresponding to the second photoluminescence material layer 20 areturned off while the two rows of first LEDs 12 corresponding to thefirst photoluminescence material layer 18 remain on. Conversely, if aemission product 36 having a CCT with a cool blueish is color isdesired, some or all of the first LEDs 12 corresponding to the firstphotoluminescence material layer 18 may be turned off while the two rowsof second LEDs 14 corresponding to the second photoluminescence materiallayer 20 remain on.

Thus, by configuring the control circuit 40 of the white light emittingdevice 10 to translate output power of the dimmer switch 38 into acorresponding on/off configuration of the two rows of first LEDs 12 andthe two rows of second LEDs 14, the white light emitting device 10 maybe tuned like a typical incandescent light bulb.

Alternatively, in another embodiment, instead of an on/off control,individual power levels (typically current) are adjusted by the controlcircuit 40 to the two rows of first LEDs 12 and the two rows of secondLEDs 14, so that a selected ratio of the emissions λ₂, λ₃ from the firstand second photoluminescence material layers 18, 20 is obtained togenerate a desired CCT of the emission product 36. In this approach, theCCT of the emission product 36 corresponds to a cool blueish white coloror a warm yellowish white color depending upon the relative amounts ofpower that are provided to the two rows of first LEDs 12 and the tworows of second LEDs 14.

With reference to FIGS. 3A and 3B, there is shown a plan view of a whitelight emitting device 310 in accordance with an embodiment of theinvention, and a cross section side view through A-A (of FIG. 3A). Thewhite light emitting device 310 is similar to the white light emittingdevice 10 of FIG. 1. Therefore, like reference numerals are used in FIG.3 to denote like features.

In this embodiment, the white light emitting device 310 has a circularshape. Thus, the substrate 316 is planar and disk shaped. Forminganother chip on board arrangement, alternating arrays (rows) of firstLEDs 312 and second LEDs 314 are configured from one circumferentialpoint 342 to the diametrically opposing circumferential point 344. Inthis embodiment, the arrays are in the form of rows. As illustrated, thecircular substrate 316 comprises a total of seven rows of alternatingarrays of first LEDs 312 and second LEDs 314, wherein the first andsecond LEDs 312, 314 are substantially symmetrically distributed overthe entirety on the circular substrate 316. The circular substrate 316also comprises about its entire perimeter a wall 326 which encloses allthe arrays of first LEDs 312 and second LEDs 314. In this embodiment,the first and second LEDs 312, 314 are InGaN (indium gallium nitride)blue LEDs which are operable to generate blue light having a peakwavelength in a wavelength range 400 to 480 nm (typically 450 to 470nm).

A first photoluminescence material layer 318 comprising a first phosphormaterial (typically green and red emitting phosphor materials) isdeposited onto the circular substrate 316 and, in this embodiment,completely covers the arrays of first LEDs 312. The first phosphormaterial is excitable to generate white light having a correlated colortemperature of about 2700K to 3500K (warm white light). Similarly, thesecond photoluminescence material layer 320 comprising a second phosphormaterial (typically a green phosphor material) is deposited onto thecircular substrate 316 and, in this embodiment, completely covers thearrays of second LEDs 314. The second phosphor material is excitable togenerate white light having a correlated color temperature of 5000K to6500K (cool white light). In this way, the first and secondphotoluminescence material layers 18, 20 are located adjacent oneanother and also contained within the upright walls 26. In this way, thewhite light emitting device 310 comprises a total of seven alternatingstrips of the first and second photoluminescence material layers 18, 20associated with the alternating arrays of first and second LEDs 312,314.

A circular and planar diffusing layer 322, having slightly smallerdimensions to those of the circular substrate 316, is disposed over andon top of both the first photoluminescence material layer 318 and secondphotoluminescence material layer 320, and is also contained inside theupright wall 26. The upper surface 328 of the upright wall 326 togetherwith the upper surface 330 of the circular diffusing layer 322 define aflush surface. The circular diffusing layer 322, the circular substrate316, and wall 326 define an interior volume 332 which houses andencloses the first and second photoluminescence material layers 18, 20and the alternating arrays of first LEDs 312 and second LEDs 314.

A method of manufacturing the white light emitting device 310, forexample, comprises the steps of: providing an array of first LEDs 312;dispensing a first photoluminescence material layer 318 at least oversaid array of first LEDs 312; providing an array of second LEDs 314;dispensing a second photoluminescence material layer 320 at least oversaid array of second LEDs 314; and dispensing a diffusing layer 322 oversaid first and second photoluminescence material layers 318, 320. Inthis embodiment, the diffusing layer 322 is in direct contact with thefirst and second photoluminescence material layers 318, 320. Although,it will be appreciated that, in other embodiments, the diffusing layermay be in direct contact with only the first or second photoluminescencematerial layer.

The white light emitting device 310, to an observer 334, exhibitsenhanced color uniformity of generated white light due to thecombination of the first and second photoluminescence material layers18, 20 and the diffusing layer 322 disposed thereover. Compared with CSPLEDs, for example, the amount of photoluminescence material used mayalso be reduced thereby providing a more cost-effective manner ofmanufacturing the white light emitting device 310. This is because thediffusing layer 322 comprising light scattering particles 324 increasesthe probability that a photon will result in the generation ofphotoluminescence light by directing light back into the first or secondphotoluminescence layers. Thus, the amount of photoluminescence materialrequired to generate a given color temperature of light can be reducedsince more of the first/second LED 312, 314 light is converted tophotoluminescence light owing to the diffusing layer 322.

Table 1 tabulates values for a white light emitting device without adiffusing layer. More particularly, the white light emitting devicecomprises a first LED and a second LED disposed on a substrate, a firstphotoluminescence material layer disposed over at least said first LED,a second photoluminescence material layer disposed over at least saidsecond LED. The device having a nominal correlated color temperature(CCT) of 2700 K. A first batch containing six samples of the devicewithout a diffusing layer were prepared and tested, and the parameterdata including light intensity (lm), luminous efficacy LE (lm/W),chromaticity CIE x,y, CRI-Ra, and CRI-R9 for each sample is shown inTable 1 together with an average value for each parameter.

TABLE 1 White light emitting device performance without a diffusinglayer Intensity LE Chromaticity CCT CRI Number (lm) (lm/W) CIE x CIE y(K) Ra R9 1 1980.0 112.1 0.4631 0.4216 2740 95.0 67.3 2 1991.0 112.80.4632 0.4212 2735 95.1 68.0 3 2007.0 113.8 0.4636 0.4212 2729 95.2 68.44 1979.0 112.3 0.4628 0.4210 2740 95.0 67.4 5 1976.0 113.3 0.4626 0.41952731 95.5 69.5 6 1979.0 112.5 0.4618 0.4203 2747 94.7 66.4 Avg 1985.3112.8 0.4629 0.4208 2737 95.1 67.8

Table 2 tabulates values for a white light emitting device having a 5%wt diffusing layer. More particularly, the white light emitting devicecomprising a first LED and a second LED disposed on a substrate, a firstphotoluminescence material layer disposed over at least said first LED,a second photoluminescence material layer disposed over at least saidsecond LED, and a diffusing layer disposed over said first and secondphotoluminescence layers, said diffusing layer comprising lightscattering particles. The 5% wt diffusing layer denotes a loading of 5weight percent of scattering particles in 95 weight percent liquidsilicone (e.g. light transmissive material). The device having a nominalcorrelated color temperature (CCT) of 2700 K. The first batch containingsix samples of the device with a 5% wt diffusing layer were prepared andtested, and the parameter data including light intensity (lm), CIE x,y,CRI-Ra, and CRI-R9 for each sample is shown in Table 2 together with anaverage value for each parameter.

TABLE 2 White light emitting device performance without a diffusinglayer Intensity LE Chromaticity CCT CRI Number (lm) (lm/W) CIE x CIE y(K) Ra R9 1 1960.0 110.85 0.4668 0.4247 2712 94.4 64.7 2 1980.0 112.020.4669 0.4240 2705 94.6 65.3 3 1990.0 112.84 0.4674 0.4243 2701 94.665.7 4 1960.0 111.22 0.4665 0.4243 2713 94.4 64.4 5 1950.0 111.79 0.46640.4228 2703 94.9 66.5 6 1960.0 111.38 0.4656 0.4235 2720 94.2 63.6 Avg1966.7 111.68 0.4666 0.4239 2709 94.5 65.0

Comparing the average data values of Tables 1 and 2, it can be seen thatby including a 5% wt diffusing layer there is a negligible change in CIEx (0.46289 compared with 0.4666), CIE y (0.4208 compared with 0.4239),CRI-Ra (95.1 compared with 94.5), and CRI-R9 (67.8 compared with 65.0).Tables 1 and 2 also show that there is only a negligible change in lightintensity (1985.3 lm compared with 1966.7 lm) and luminous efficacy(112.8 lm/W compared with 111.7 lm/W). Therefore, the data demonstratesthat the performance and characteristics of the white light emittingdevice do not degrade with the inclusion of a 5% wt diffusing layer.However, the observer will observe a significant improvement in thecolor uniformity of light generated by the white light emitting deviceformed according to the invention, compared with a device devoid of adiffusing layer. The inventors have also found that the white lightemitting device of the present invention advantageously has a superiorlight intensity output and luminous efficacy than an equivalent deviceutilizing CSP LEDs without a diffusing layer.

Table 3 tabulates values for a white light emitting device without adiffusing layer. More particularly, the white light emitting devicecomprises a first LED and a second LED disposed on a substrate, a firstphotoluminescence material layer disposed over at least said first LED,a second photoluminescence material layer disposed over at least saidsecond LED. The device having a nominal correlated color temperature(CCT) of 2700 K. A second batch containing six samples of the devicewithout a diffusing layer were prepared and tested, and the parameterdata including light intensity (lm), efficacy (lm/W), CIE x,y, CRI-Ra,and CRI-R9 for each sample is shown in Table 3 together with an averagevalue for each parameter.

TABLE 3 White light emitting device performance without a diffusinglayer Intensity LE Chromaticity CCT CRI Number (lm) (lm/W) CIE x CIE y(K) Ra R9 7 1958.0 111.4 0.4641 0.4217 2726 95.1 68.1 8 1991.0 113.40.4628 0.4214 2742 95.0 67.3 9 1953.0 110.7 0.4631 0.4199 2726 95.5 69.410 1994.0 113.1 0.4630 0.4216 2741 94.9 67.3 11 2000.0 113.1 0.46470.4211 2714 94.8 65.5 Avg 1979.2 112.3 0.4635 0.4211 2730 95.1 67.5

Table 4 tabulates values for a white light emitting device having a 10%wt diffusing layer. More particularly, the white light emitting devicecomprising a first LED and a second LED disposed on a substrate, a firstphotoluminescence material layer disposed over at least said first LED,a second photoluminescence material layer disposed over at least saidsecond LED, and a diffusing layer disposed over said first and secondphotoluminescence layers, said diffusing layer comprising lightscattering particles. The 10% wt diffusing layer denotes a loading of 5weight percent of scattering particles in 90 weight percent liquidsilicone (e.g. light transmissive material). The device having a nominalcorrelated color temperature (CCT) of 2700 K. The second batchcontaining six samples of the device with a 10% wt diffusing layer wereprepared and tested, and the parameter data including light intensity(lm), efficacy (lm/W), CIE x,y, CRI-Ra, and CRI-R9 for each sample isshown in Table 4 together with an average value for each parameter.

TABLE 4 White light emitting device performance without a diffusinglayer Intensity LE Chromaticity CCT CRI Number (lm) (lm/W) CIE x CIE y(K) Ra R9 7 1920.0 109.2 0.4720 0.4260 2653 94.5 64.6 8 1940.0 110.40.4711 0.4258 2663 94.3 63.8 9 1910.0 108.2 0.4713 0.4243 2650 94.9 65.910 1950.0 110.5 0.4713 0.4259 2662 94.4 64.0 11 1960.0 110.7 0.47290.4253 2636 94.9 66.8 Avg 1936.0 109.8 0.4717 0.4246 2653 94.6 65.0

Comparing the average data values of Tables 3 and 4, it can be seen thatby including a 10% wt diffusing layer there is only a negligible changein CIE x (0.4635 compared with 0.4717), CIE y (0.4211 compared with0.42456), CRI-Ra (95.1 compared with 94.6), and CRI-R9 (67.5 comparedwith 65.0). Tables 3 and 4 also show that there is only a negligiblechange in light intensity (1985.3 lm compared with 1966.7 lm) andluminous efficacy (112.3 lm/W compared with 109.8 lm/W). Therefore, thedata demonstrates that the performance and characteristics of the whitelight emitting device do not degrade with the inclusion of a 10% wtdiffusing layer. However, the observer will observe a significantimprovement in the color uniformity of light generated by the whitelight emitting device formed according to the invention, compared with adevice devoid of a diffusing layer.

Referring to FIG. 4, there is shown a white light emitting device 410formed according to an embodiment of the invention. The white lightemitting device 410 is the same as the white light emitting device 310shown in FIG. 3A except that it comprises fewer first and second LEDs412, 414. More particularly, the first and second LEDs 412, 414 aresubstantially non-symmetrically (non-uniformly) distributed. Despite,the non-symmetrical distribution, the observer 434 (not shown) exhibitsenhanced color uniformity of generated white light due to thecombination of the first and second photoluminescence material layers418, 420 and the diffusing layer 422 (not shown) disposed thereover.Compared with CSP LEDs, for example, the amount of photoluminescencematerial used may also be reduced thereby providing a morecost-effective manner of manufacturing the white light emitting device410. This is because the diffusing layer 422 (not shown) comprisinglight scattering particles 424 (not shown) increases the probabilitythat a photon will result in the generation of photoluminescence lightby directing light back into the first or second photoluminescencelayers 418, 420. Thus, the amount of photoluminescence material requiredto generate a given color temperature of light can be reduced since moreof the first/second LED 412, 414 light is converted to photoluminescencelight owing to the diffusing layer 422 (not shown).

Referring to FIG. 5, there is shown a side sectional view of anembodiment of a diffusing layer 522. The diffusing layer 522 has arectangular cross section and is essentially planar in form. Thediffusing layer 522 comprises a light transmissive material 546 andlight scattering particles 524. In this embodiment, the light scatteringparticles 524 are incorporated in the light transmissive material 546and are substantially uniformly distributed through the lighttransmissive material 546. However, it will be appreciated that in otherembodiments the light scattering particles may not be uniformlydistributed in a light transmissive medium/material. The lightscattering particles 524 can have an average particle size selected suchthat they scatter excitation light generated by the first and secondLEDs relatively more than they scatter light generated by the first andsecond photoluminescence material layers, and in this embodiment theaverage particle size being in a range from about 100 nm to about 200nm. The light scattering particles 524 are formed from titanium dioxideor other materials as defined herein.

Referring to FIG. 6, there is shown a side sectional view of anotherembodiment of a diffusing layer 622. Similar to the embodiment of FIG.5, the diffusing layer 622 has a rectangular cross section and isessentially planar in form. However, in this embodiment the diffusinglayer 622 comprises a layer of the light transmissive material 648 and alayer of the light scattering particles 650. The layer of lightscattering particles 650 may be formed in accordance with the diffusinglayer 522 of FIG. 5, for instance. As shown in FIG. 6, the layer of thelight transmissive material 648 is directly in contact with and disposedabove the layer of the light scattering particles 650 so that the layerof the light transmissive material 648 appears closest to the observer634.

Referring to FIG. 7, there is shown a side sectional view of thediffusing layer 622 of FIG. 6 directly in contact with and disposedabove alternating strips of first and second photoluminescence materiallayers 718, 720 (partially shown in FIG. 7). In this arrangement, asseen from an observer 734, the layer of light transmissive material 648is the outermost layer and faces outwardly towards the observer 734.More particularly, the layer of the light scattering particles 650 isdisposed between the layer of the light transmissive material 648 andthe alternating strips of first and second photoluminescence materiallayers 718, 720. In such a configuration, the layer of lighttransmissive material 648 may act as a protective layer to the layer ofthe light scattering particles 650 and the alternating strips of firstand second photoluminescence material layers 718, 720.

Referring to FIG. 8, there is shown a side sectional view of analternative embodiment of a diffusing layer 822 directly in contact withand disposed above alternating strips of first and secondphotoluminescence material layers 818, 820 (partially shown in FIG. 8).The diffusing layer 822 is the same as the diffusing layer 622 of FIGS.6 and 7, except that the layer of the light scattering particles istransposed with the layer of the light transmissive material. Hence, inthis arrangement, as seen from an observer 834, the layer of the lightscattering particles 850 is the outermost layer and faces outwardlytowards the observer 834. More particularly, the layer of the lighttransmissive material 848 is disposed between the layer of the lightscattering particles 850 and the alternating strips of first and secondphotoluminescence material layers 818, 820. In such a configuration,provides greater distance between the layer of light scatteringparticles 850 and the first and second photoluminescence material layers818, 820.

Referring to FIG. 9, there is shown a side sectional view of a diffusinglayer 922 in accordance with another embodiment of the invention. Inthis embodiment, the diffusing layer 922 comprises two layers of thelight transmissive material 948 and a layer of the light scatteringparticles 950 disposed therebetween. This configuration provides agreater distance between the layer of light scattering particles 950 andthe first and second photoluminescence material layers 918,920, as wellas the layers of light transmissive material 948 acting as a protectivelayer.

Referring to FIG. 10, there is shown a side sectional view of adiffusing layer 1022 in accordance with another embodiment of theinvention. In this embodiment, the diffusing layer 1022 is the same asthe diffusing layer 522 of FIG. 5, except the diffusing layer 1022 has adifferent shape (Convex shape). The diffusing layer 1022 has a shapehaving a cross section which is rectangular with an arch along one ofits longer sides. Thus, the cross section defines a shape in which thethickness of the diffusing layer 1022 varies across its width. Ofcourse, it will be appreciated that the thickness of the diffusing layermay vary across its length, in other embodiments. In this way, theamount of light scattering particles 1024 may vary across the diffusinglayer 1022. For instance, in this embodiment, there are more lightscattering particles 1024 towards the center of the light diffusinglayer 1022 than its edges. By varying the thickness of the lightdiffusing layer 1022, the light scattering properties can beappropriately selected depending on the desired output of the whitelight emitting device with which it is utilized.

Referring to FIG. 11, there is shown a side sectional view of adiffusing layer 1122 in accordance with another embodiment of theinvention. In this embodiment, the diffusing layer 1122 is the same asthe diffusing layer 522 of FIG. 5, except the diffusing layer 1122 has adifferent distribution of light scattering particles 1124 within thelight transmissive material 1146. In this embodiment, the lightscattering particles 1124 are incorporated in the light transmissivematerial 1146 and are not uniformly distributed through the lighttransmissive material 1146. Instead, in this embodiment, theconcentration of light scattering particles 1124 within the diffusinglayer 1124 varies along its width. Of course, it will be appreciatedthat the concentration of light scattering particles 1124 within thediffusing layer 1124 may vary across its length, in other embodiments.In this way, the amount of light scattering particles 1124 may varyacross the diffusing layer 1122. For instance, in this embodiment, thereis a higher concentration of light scattering particles 1124 towards thecenter of the light diffusing layer 1122 than its edges. By varying theconcentration of light scattering particles 1124 in the light diffusinglayer 1022, the light scattering properties can be appropriatelyselected depending on the desired output of the white light emittingdevice with which it is utilized.

FIG. 12 is a sectional view of the diffusing layer 522 of FIG. 5directly in contact with and disposed above alternating strips of firstand second photoluminescence material layers 1218, 1220 (partially shownin FIG. 12). In this embodiment, while the diffusing layer 522 compriseslight scattering particles 524, the first photoluminescence materiallayer 1218 also comprises light scattering particles 1252. This mayimprove the uniformity of the white light generated by the lightemitting device generated still further.

FIG. 13 is a sectional view of the diffusing layer 522 of FIG. 5directly in contact with and disposed above alternating strips of firstand second photoluminescence material layers 1318, 1320 (partially shownin FIG. 13). In this embodiment, while the diffusing layer 522 compriseslight scattering particles 524, the first and second photoluminescencematerial layers 1318, 1320 also comprise light scattering particles1352, 1354 respectively. This may improve the uniformity of the whitelight generated by the light emitting device generated even further.

Referring to FIG. 14, there is shown a component 1456 and a separate LEDarray 1458 for a white light emitting device in accordance with anembodiment of the invention. In this embodiment, the component 1456comprises a diffusing layer 1422 disposed over alternating strips offirst and second photoluminescence material layers 1418, 1420. Thediffusing layer 1422 comprising a layer of light scattering particles1450 and a layer of light transmissive material 1448. In thisembodiment, the alternating strips of first and second photoluminescencematerial layers 1418,1420 are in direct contact with the layer of lighttransmissive material 1448 of the diffusing layer 1422, such that thelayer of light transmissive material 1448 is disposed between the layerof light scattering particles 1450 and the alternating strips of firstand second photoluminescence material layers 1418, 1420.

The first photoluminescence material layer 1418 comprises a firstphosphor material excitable to generate white light having a correlatedcolor temperature of 2700K, and the second photoluminescence materiallayer 1420 comprises a second phosphor material excitable to generatelight having a correlated color temperature of 5000K.

There is also shown a separate LED array 1458 having an alternatingarray of first and second LEDs 1412,1414 disposed on a substrate 1416.

The component 1456 and LED array 1458 function in the manner describedherein. The component 1456 may be assembled with the LED array 1458 inthe direction indicated by arrows 1460 so that the alternating strips ofthe first and second photoluminescence material layers 1418, 1420 can beassociated with the alternating arrays of first LEDs and second LEDs1412, 1414.

It will be appreciated that the present invention is not restricted tothe specific embodiments described and that variations can be made thatare within the scope of the invention.

1. A white light emitting device comprising a first LED and a second LEDdisposed on a substrate, a first photoluminescence material layerdisposed over at least said first LED, a second photoluminescencematerial layer disposed over at least said second LED, and a diffusinglayer disposed over said first and second photoluminescence layers, saiddiffusing layer comprising light scattering particles.
 2. The Whitelight emitting device of claim 1, wherein the first photoluminescencematerial layer comprises a first phosphor material and/or the secondphotoluminescence material layer comprises a second phosphor material.3. The white light emitting device of claim 2, wherein the firstphosphor material is excitable to generate white light having acorrelated color temperature of 2700K to 3500K.
 4. The white lightemitting device of claim 2, wherein the second phosphor material isexcitable to generate white light having a correlated color temperatureof 5000K to 6500K.
 5. The white light emitting device of claim 1,comprising alternating arrays of first LEDs and second LEDs.
 6. Thewhite light emitting device of claim 5, comprising alternating strips ofthe first and second photoluminescence material layers associated withthe alternating arrays of first LEDs and second LEDs.
 7. (canceled) 8.The white light emitting device of claim 1, wherein the diffusing layercomprises a light transmissive material and light scattering particles.9. (canceled)
 10. The white light emitting device of claim 8, whereinthe light scattering particles are substantially uniformly distributedthrough the light transmissive material.
 11. The white light emittingdevice of claim 8, wherein the diffusing layer comprises a layer of thelight transmissive material and a layer of the light scatteringparticles.
 12. The white light emitting device of claim 11, wherein thelayer of the light transmissive material is disposed between the layerof the light scattering particles and the first and/or secondphotoluminescence material layers.
 13. The white light emitting deviceof claim 11, wherein the layer of the light scattering particles isdisposed between the layer of the light transmissive material and thefirst and/or second photoluminescence material layers.
 14. (canceled)15. The white light emitting device of claim 1, wherein at least one ofthe first photoluminescence material layer, the second photoluminescencematerial layer, or the diffusing layer comprises light scatteringparticles.
 16. (canceled)
 17. The white light emitting device of claim1, wherein the substrate comprises a circuit board, optionally a metalcore printed circuit board.
 18. (canceled)
 19. (canceled)
 20. (canceled)21. The white light emitting device of claim 20, wherein the thicknessor concentration of the diffusing layer varies.
 22. (canceled) 23.(canceled)
 24. The white light emitting device of claim 1, wherein theweight percent loading of the light scattering particles is from 0.1 to50% wt or from 5 to 10% wt.
 25. (canceled)
 26. A method of manufacturinga white light emitting device, comprising the steps of: providing anarray of first LEDs; dispensing a first photoluminescence material layerat least over said array of first LEDs; providing an array of secondLEDs; dispensing a second photoluminescence material layer at least oversaid array of second LEDs; and dispensing a diffusing layer over saidfirst and second photoluminescence material layers.
 27. A white lightemitting device comprising alternating arrays of first LEDs and secondLEDs disposed on a substrate, a first photoluminescence material layerdisposed over at least said array of first LEDs, a secondphotoluminescence material layer disposed over at least said array ofsecond LEDs, and a diffusing layer disposed over said first and secondphotoluminescence material layers, the diffusing layer comprising lightscattering particles, wherein the first photoluminescence material layercomprises a first phosphor material excitable to generate white lighthaving a first correlated color temperature, the secondphotoluminescence material layer comprises a second phosphor materialexcitable to generate white light having a second correlated colortemperature.
 28. The white light emitting device of claim 27, whereinthe first correlated color temperature is from 2700K to 3500K and/or thesecond correlated color temperature is from 5000K to 6500K.
 29. Acomponent for a white light emitting device, comprising alternatingstrips of first and second photoluminescence material layers disposed ona substrate, and a diffusing layer disposed over said alternating stripsof first and second photoluminescence material layers, the diffusinglayer comprising light scattering particles, wherein the firstphotoluminescence material layer comprises a first phosphor materialexcitable to generate white light having a first correlated colortemperature, and the second photoluminescence material layer comprises asecond phosphor material excitable to generate light having a secondcorrelated color temperature.
 30. The component of claim 29, wherein thefirst correlated color temperature is from 2700K to 3500K and/or thesecond correlated color temperature is from 5000K to 6500K.